Electronic structure and magnetic properties of RMnX (R=Mg, Ca, Sr, Ba, Y; X=Si, Ge) studied by KKR method

Electronic structure calculations, using the charge and spin self-consistent Korringa- Kohn-Rostoker (KKR) method, have been performed for several RMnX compounds (R=Mg, Ca, Sr, Ba, Y; X=Si, Ge) of the CeFeSi-type structure. The origin of their magnetic properties has been investigated emphasizing the role of the Mn sublattice. The significant influence of the Mn-Mn and Mn-X interatomic distances on the Mn magnetic moment value is delineated from our computations, supporting many neutron diffraction data. We show that the marked change of <InlineEquation ID="Equ1"> <EquationSource Format="TEX">$\mu_{\rm Mn}$</EquationSource> </InlineEquation> with the Mn-Mn and Mn-X distances resulted from a redistribution between spin-up and spin-down d-Mn DOS rather than from different fillings of the Mn 3d-shell. The obtained KKR results are discussed considering the Stoner-like and covalent magnetism effects. From comparison of electronic structure of RMnX in different magnetic states we conclude that the antiferromagnetic coupling in the Mn (001) plane considerably increases the Mn magnetic moment with respect to the ferromagnetic arrangement. Bearing in mind that the neutron diffraction data reported for the RMnX compounds are rather scattered, the KKR computations of <InlineEquation ID="Equ2"> <EquationSource Format="TEX">$\mu_{\rm Mn}$</EquationSource> </InlineEquation> are in fair agreement with the experimental values. Comparing density of states near E <Subscript> F </Subscript> obtained in different magnetic orderings, one can notice that the entitled RMnX systems seem to ‘adapt’ their magnetic structures to minimize the DOS in the vicinity of the Fermi level. Noteworthy, the SrMnGe antiferromagnet exhibits a pseudo-gap behaviour at E <Subscript> F </Subscript>, suggesting anomalous electron transport properties. In addition, the F-AF transition occurring in the disordered La<Subscript>1-x </Subscript>Y<Subscript> x </Subscript>MnSi alloy for the 0.8 > x > 1 range is well supported by the DOS features of La<Subscript>0.2</Subscript>Y<Subscript>0.8</Subscript>MnSi. This latter result sheds light on the magnetic structure of the YMnSi compound. In contrast to the investigated RMnX compounds, YFeSi was found to be non-magnetic, which is in excellent agreement with the experimental data. Copyright Springer-Verlag Berlin/Heidelberg 2004